April 11 (UPI) — Facebook CEO Mark Zuckerberg will testify on Wednesday before the House Energy and Commerce Committee about a recent data breach that affected millions of the site’s users.

His testimony is scheduled to begin at 10 a.m. EST. Lawmakers are expected to ask Zuckerberg about the Cambridge Analytica data breach that resulted in the disclosure of personal information belonging to possibly 87 million people.

On Tuesday, the Facebook chief defended his company’s response to the breach and apologized for not going far enough to protect user privacy.

“We took down the app, and we demanded that both the app developer and Cambridge Analytica delete and stop using any data that they had,” Zuckerberg said. “They told us that they did this. In retrospect, it was clearly a mistake to believe them.”

Zuckerberg pledged to “conduct a full audit” of Facebook apps that the company determines to be suspicious and said one of his “greatest regrets” was his company’s slow response to pinpoint Russian bad actors on Facebook during that election cycle.

Facebook has taken steps to make it easier for users to control what they share and delete collected data. On Monday, the site began allowing users to see if their information was shared with Cambridge Analytica.